Freshwater Aquarium MaintenanceFishtank Forum for the discussion of maintenance practices in a Freshwater environment. This includes questions on testing parameters, performing water changes, cleaning algae, replacing substrates, moving tanks, and any other maintenance related tasks for Freshwater aquariums.

Now that I?m paying attention to KH and GH, (just a few months ago I didn't know what they stood for) I?m trying to figure out what is a good KH level?

As is often pointed out, using just RO water for FW tanks (like have been doing for years) is not a good thing. I?ve started mixing in a little straight tap water (from my well before it goes through the water softener) to add buffering.

The other day while I was testing my tanks I also tested my tap water. The guy at the LFS mentioned that the local Indiana water might as well as be solid rock because of the hardness. My well water tested with a KH of 18 and I gave up on the GH at 20. (Everyone should test their source water BEFORE they start pouring it in the tank).

gH and kH are very dependant on what you keep, if you want to get serious you can research what the native water parameters are of the fish you keep, but in all reality 95% of the fish we keep are farm raised so we can keep them at awfully different params then in the wild. Many fish will "color up" better or breed in certain water conditions. Long story short it depends on your fish. As long as the kH is over 3dkH it should be buffered

It is my understanding that GH (General Hardness) and KH (Carbonate Hardness) both help to maintain a stable PH (Power of Hydrogen).

GH refers to the dissolved concentration primarily of magnesium and calcium which are important for the fish's internal osmotic process. I believe a reading of 100-200 is best, as anything over that causes respiration problems.

KH is basically the buffering capacity of your aquarium. I believe that should be maintained over 80 in order to prevent a sudden drop in PH. Below that allows for shifts in PH.

That is my take on it. I would suspect there are more technical descriptions but that is how I know it.

OK. I found a very technical explaination from a chemist on this topic. Here are just a few parts about the pH & KH FYI:

pH: the measure of H+ ions in the water, based on a logarithmic scale. Implicitly, this can also be defined as the relative difference between H+ and OH- ions. At a pH of 7, these two ions are expected to be in fully equal proportions. At pH's lower than 7, the number of H+ ions is greater than the number of OH- ions which is called an acidic condition. The opposite is true at pH's above 7, which is called a basic condition.

Alkalinity: refers to a solution's ability to neutralize H+ ions (strictly speaking, this term is only in relation to carbonate equivalence points). This is related to buffering capacity, which refers to a solution's resistance to a change in pH -- its ability to keep the H+ and OH- ions at a particular balance. The important thing to note is that alkaline does not mean a pH above 7 or mean non-acidic. It's frequently used that way, but that's incorrect and more importantly it's quite confusing. As stated above, a pH above 7 is properly referred to as basic.

Carbonate Hardness (KH): Is a means of measuring alkalinity, but in a somewhat complicated way. It's designed so that one ppm of carbonate is worth two ppm of bicarbonate, and carbonic acid is not accounted for at all. In other words, it basically measures your water's ability to absorb H+ ions through carbonates (their ability to resistant a drop in pH). If the pH of your water is about 8.2 - where ~100% of the carbonates are in bicarbonate form - then KH is also equal to the ability of carbonates to release H+ ions (their ability to resist an increase in pH). If your pH is some other value, you will have to calculate this value yourself - a pH lower than ~8.2 will have a greater ability to resist an increase in pH than KH states while a pH above ~8.2 will have a lower ability than KH states. It is not supposed to take into account other buffers at all, so if you add phosphate buffers it will not change KH.

OK. This is VERY technical.

But what I gather is the KH reading you target depends on your pH target. And as Dr.Fragenstein points out that it all depends on your fish selection. Elsewhere I read pH really only depends if the fish is Wild caught, not commercialy bred.

So I conclude a KH target of 5 should, um, be a wild guess.

When I looked up some of the fish I have they show a KH range of 2 -20 so I guess the KH doesn't effect the fish that much.

just a quick fyi....it is pH, not PH....and it stands for the potential of hydrogen being in the water.....in other words are the conditions right for hydrogen or or are they not....the potential for it's presence. The capital H in this case is the symbol from the table of elements and that is why it is capitalized and the p is not.

Just a quick fyi....it is pH and not PH and it is potential for hydrogen.....in other words are the conditions right to allow for the presence of hydrogen and how much. So a higher pH has a higher potential of hydrogen in the water (or other liquid).

Also the levels depend on whether or not you have a planted tank and it looks like you do. The plants require a certain amount of dissolved minerals. Do you use CO2? Do you fertilize? Do you test nitrate and iron levels regularly. Generally between 6-8 degrees of hardness for both (KH and GH)should be adequate for your plants. It would be better to have one test kit that tests specifically for each parameter. Make your changes slowly....if your tank has managed this long, a slow change is better for your fish.

You want to be very careful about adding things to the tank in an effort to adjust things like the pH. It can often cause secondary problems....like adding phosphates to lower the pH will kill your plants. It is also important to monitor all nutrient levels....if the nutrients are too low, the plants will not do well, but the algae will thrive. When the nutrient levels are at the correct level, (and there is adequate CO2 and adequate lighting) the plants will out compete the algae for the nutrients. The plants will grow, the algae will starve. You will still get some algae, but that can be managed by a good cleaning crew (snails, Otos, SAE's etc)

I too use RO water mixed with my tap water (well water we live on a farm) If you are using city water you have to be very careful as they have to put lots of harsh chemicals in it. You can get products like Seachem's Equalibrium to put the minerals back in the RO water. But this will not address the alkalinity, KH, this only affects the GH. To increase alkalinity, you can use baking soda (sodium bicarbonate) I believe the website below talks about this as well. If you are not using CO2 you may not need to increase your alkalinity very much if you are doing regular water changes. I did notice that after I started using CO2, my pH became much more stable with only minimal ups and downs that coincide with the day / night schedule.

I used to test my pH with the regular liquid test kits, but found them to be unreliable in that different manufacturers would give me two different results. I now use a Pinpoint monitor that gives me an accurate reading at all times. Then by testing the KH, I can know how much dissolved carbon is in the water through a chart posted on the following website (and other places). This website has some very good information for planted aquariums, water levels etc. By maintaining appropriate CO2 levels and nutrient levels, I have more than doubled my plant growth and my tanks have dropped in the amount of algae. I used to have to scrape the glass each week to keep it reasonably good looking. It is so much better. For my CO2 I am using Nutra fin Natural plant system. It has a great little bubble ladder that allows for maximum dissipation of the CO2 into the water. It takes a little more monitoring and fussing than an automatic set up, but for smaller tanks it seems to do a nice job. The instructions say the product is meant for 10, 15 and 20 gallon tanks (there are adjustments on the ladder), but I have experimented a little, (with the help of the recipe I found on the website below) and believe you could use this on a larger tank possibly up to a 35 gallon by mixing your own bakers yeast solution at a little stronger rate. (NutraFin uses yeast and sugar to ferment and produce the CO2). There are also instructions on the website below to make your own. I just really like their bubble ladder which you can buy separately with the tubing. Using this system will not give you the lush tropical growth that an automatic system will, but it will improve the growth and health of your tank. You should also be aware that you cannot turn it off at night so you really have to monitor it closely until you get used to what it is doing. At night when the lights go out that plants produce CO2. That along with the continued input of CO2 will naturally cause the pH to drop. You want to watch this closely until you get used to the system that it does not drop too far.

This does seem to cover more than what you were asking for.....but you can not believe what I have been through with my tanks before I figured all this out.....hope it is helpful.

Sorry about the faux pas. I didnt realize it was considered an advertisement. *Link removed per FTF Policy regarding Advertisement

Last edited by louistheloach; 09-15-2008 at 09:53 PM.
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I used to test my pH with the regular liquid test kits, but found them to be unreliable in that different manufacturers would give me two different results. I now use a Pinpoint monitor that gives me an accurate reading at all times.

Interesting that you find the liquid test kits unreliable. I've probably had more problems with pH kits going bad after a year or two than any other I use.

I looked up the Pinpoint monitor and noticed that you have to replace the probes. I have 5 tanks running now so if I got one how long would a probe last testing the different tanks?

I generally use my test results to track changes so I know when to do water changes (to hopefully to avoid large swings in anything). Accuracy is not as important to me as long as my fish are doing OK.

I cant remember how long they said the probes would last, and I dont know what I did with the directions, but I think the info is on the website of the manufacturer. I have had it for several months. I just leave it in my main tank and when I need to test the other two I move it. Soon I will have the three tanks into one.......that will be much easier to care for.

But you do have to calibrate about once a month. This involves putting the probe into two different test solutions and turning the screw until it maintains the pH of the test solution. I didnt do it for the first couple of months. It was off by <.1 ....so you may not have to calibrate each month if accuracy is not critical.

If I find my instructions, I will post the answer as to the length of use.